Stabilized sulfur-containing resins, such as polyphenylene sulfide and method of producing the same

ABSTRACT

Sulfur-containing polymers, such as polyphenylene sulfide are stabilized from releasing sulfur-containing exhaust gases by adding an additive polymer having at least one reactive radical selected from the group consisting of amino radicals, amido radicals, imido radicals, and keto radicals therein, and which is of approximate the same thermal stability as the sulfur-containing polymer, to such sulfur-containing polymer. In other embodiments of the invention, sulfur-stabilization is also achieved by incorporating suitable fundamental building blocks of the additive polymer into the sulfur-containing polymer chain in the form of reactive monomers. Further, in other embodiments, additive polymers or oligomers (so-called telecheles) having reactive radicals at their ends can be introduced into the sulfur-containing polymer chain as copolymers. In addition, low molecular weight compounds having high boiling points and having structures similar to the fundamental building blocks of the sulfur-containing polymers are also effective for stabilizing such polymers.

This is a division of application Ser. No. 388,179, filed June 14, 1982,now U.S. Pat. No. 4,447,581.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to stabilized sulfur-containing resins andsomewhat more particularly to a method of reducing sulfur-containingexhaust gases from sulfur-contfur-containing exhaust gases which arereleased from PPS. These exhaust gases still have a corrosive effect onmetal far below 200° C., i.e,, down into the use temperature range ofPPS (F. Quella, Kunststoffe Vol. 71, Nr. 6, 1981, page 389). Among othercomponents, these exhaust gases contain H₂ S, SO₂ and thiophenol. Thetypically added lithium carbonate only absorbs these gases above the PPSmanufacturing temperature range, having a maximum of 370° C.

SUMMARY OF THE INVENTION

The invention provides a means of stabilizing sulfur-containing resins,such as polyphenylene sulfide, by absorbing the sulfur-containingexhaust gas given off from such materials.

A suitable absorber for sulfur-containing gases must meet the followingconditions:

It must be just as thermally stable as the sulfur-containing resin;

It must be workable in approximately the same temperature range as thesulfur-containing resin;

It must have reactive acceptor groups for the sulfur-containing gases;

It must mix well with the sulfur-containing resin; and

The absorber or additive must still be economical.

In accordance with the principles of the invention, a sulfur-containingresin is stabilized by adding thereto an additive polymer containing atleast one aminic radical therein and exhibiting approximately the samethermal stability as the sulfur-containing resin. This additive polymerbonds the acidic gases so that the sulfur-containing exhaust vapors canbe readily absorbed.

Testing various polymers which are processable in the temperature rangeof PPS demonstrated that polymers with acceptor radicals or groups whichare effective in the area of low temperatures, such as amines orketones, are also surprizingly effective at higher temperatures.

An exemplary preferred embodiment of a suitable additive polymer usefulin the practice of the invention is polyvinyl carbazol (commerciallyavailable under the trademark LUVIKAN S).

Because of its presently high price, a mixture of this additive polymerin an amount up to about 1% by weight, based upon the weight of thesulfur-containing resin, is economical.

In a test at 200° C. on copper metal surfaces, in accordance with the Cumirror test of Bell Company, the corrosive exhaust vapors of a PPSpolymer admixed with a 1% mass component (by weight, based on the weightof the PPS) of polyvinyl carbazol showed a significantly lower amount ofsulfur-containing gases than identical PPS polymer provided only with 1%lithium carbonate. The same results were observed with sheet brasselectroplated with silver (stored in an enclosed space). With storageconditions extending over a week and at a concentration of polyvinylcarbazol greater than 1%, however, decomposition products of thispolymer appeared. However, the amount of polyvinyl carbazol to be addeddepends on the part to be manufactured. For example, a concentration of10% Luvikan can be meaningful or useful in very sensitive contactstructures which can absolutely not tolerate any sulfur-containinggases. Further, the upper use temperature in such an instance would beselected so as to be relatively low, for example at around 100° C.

In other tests, no decomposition products were encountered with theaddition of a polyimide (for example, such as commercially availableunder the trademark Torlon). The silvered plates were still completelybright after a week of storage in an enclosed space at 200° C.Similarly, tests with polyamides for example PA66 (such as commerciallyavailable under different trade designations like Ultramide) also yieldcorresponding results.

Similar results can be expected from other nitrogen-containing polymershaving nitrogen radicals therein and having a thermal stability similarto that of PPS, for example, from polyvinyl pyridine.

Another type of material which was tested for stabilizing PPS was aketone. In this instance, an absorption mechanism similar to the knownbisulfite addition reaction with aldehydes was first suspected. Apolyether ether ketone (PEEK, poly-1,4-oxyphenyloxy-p,p'-benzophenone)proved to be an effective absorber of sulfur-containing gases with aquality comparable to that of the aforementioned polyimide. With thistype of ketone, an admixture of 1% mass component with asulfur-containing polymer is economical. However, an addition of 0.1%already produced a sufficient effect extending over a week at 200° C.

A corresponding effect can also be expected from other polymer ketoneshaving thermal stability similar to that of sulfur-containing resins,such as PPS.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is known, donor-acceptor complexes, as in the case of polyvinylcarbazol, or addition compounds, as in the case of polyether etherketones, are not very thermally stable. Therefore, there must be anotheractive mechanism which leads to a stabilization of the thermaldecomposition products of sulfur-containing resins, such aspolyphenylene sulfide. With such polymers, one suspects a formation ofstable redicals, whereby the continued reaction of the thermally formedsulfur radicals is prevented.

Possibly, a chain disassociation thermally occurs (for example assuggested by A. B. Port and R. H. Still, IUPAC 26th Symposium onMacromolecules, Vol. 1, 1979, pp 645-648) in accordance with thefollowing schematic representation: ##STR1## attacking adjacent chains,cross-linking, accelerating decomposition, splitting-off ofsulfur-containing gases.

The stabilization mechanism, in accordance with the principles of theinvention can, for example, occur in accordance with the followingschematic representation: ##STR2## All reaction products are incapableof further accelerating the decomposition.

Since the thermal decomposition of polysulfones as well as othersulfur-containing resins occurs similarly to that of polyphenylenesulfide, an equivalent effect of the additive polymers to stabilize thesame, can be expected.

EXEMPLARY EMBODIMENT 1

Polyphenyl sulfide in granular form is admixed with pulverized additivepolymer as set forth below and the mixture is subjected to decompositionconditions at 200° C. with a flowing air stream:

    ______________________________________                                                      Amount Added                                                                              Amount of Exhaust                                                 (% Mass     Vapors in comparison                                Stabilizer:   Component)  to Ryton R4 = 1                                     ______________________________________                                        Polyether ether ketone                                                                      2           0.25                                                Polyvinyl carbazol                                                                          0.1         0.25                                                Polyvinyl carbazol                                                                          1           2.75                                                Polybutylene  0.1         0.40                                                terephthalate                                                                 Polybutylene  0.5         1.40                                                terephthalate                                                                 Polyimide (Torlon 4203)                                                                     1           0.25                                                ______________________________________                                    

The foregoing results were substantiated by means of storage tests (25 gsmall standard rods for 5 days at 200° C. in an enclosed space) onelectro-deposited silver surfaces. In contrast to Ryton R4 (acommercially available PPS having 1% mass component of lithium carbonateadmixed therein), the test specimens with lower exhaust vaporconcentrations likewise produced very slight or no tarnishing on thesilver surfaces.

During decomposition at 300° C., under synthetic air, polyether etherketone and polymide still exhibited considerable reduction ofsulfur-containing gases in comparison to Ryton R4.

EXEMPLARY EMBODIMENT 2

A PPS granulate (Ryton BR-06) was divided into three portions, with twoof the portions being thoroughly admixed with the additive polymersspecified below and each portion was worked by an injection molding andthe exhaust vapor measured at 300° C. with the following results:

    ______________________________________                                                    Amount of Amount of exhaust                                       Material    Additive  vapors (relative units)                                 ______________________________________                                        Ryton BR-06 0%        1                                                       Ryton BR-06 0.5%      0.8                                                     + Luvican                                                                     Ryton BR-06 3%        0.5                                                     + PA 66                                                                       ______________________________________                                    

EXEMPLARY EMBODIMENT 3

The amount of exhaust gas from polysulfone (PSU) was measured in thepresence of the following additives (PSU without additive=1, at 170° C.,air, measured with a sulfur detector)

    ______________________________________                                                          Amount of exhaust vapors                                    Additive          (relative units)                                            ______________________________________                                        Polyether ether ketone (1%)                                                                     0.5                                                         Polyimide (0.5%)  1.2                                                         ______________________________________                                    

The effectiveness of a stabilizer depends upon the fact that it canreach the reactive centers with sufficient rapidity. With a polymeradditive, the added polymer must either exhibit a sufficiently highchain mobility in order to engage in the decomposition process at thecorrect time or it must agglomerate to, for example, the PPS chain in amanner of a complex. The first case is conditioned by the nature of theadded polymers, the second case occurs during melting, as in injectionmolding.

A mechanism which does justice to both cases can be achieved byincorporating suitable fundamental building blocks into thesulfur-containing resin chain in the form of a co-polymer. For example,since PPS is manufactured by means of condensation, it is readilyfeasible to introduce suitable groups by means of a co-condensationreaction. During the manufacture of PPS in accordance with the followingschematic equation: ##STR3##

In addition to the dichlorobenzene and Na₂ S, a suitable comonomer couldbe added. For example: ##STR4## corresponding to the polyether ketone(PEEK) or ##STR5## corresponding to the components of a polyimide, suchas Torlon. However, the introduction of certain groups, such aspolyvinyl carbazol, is difficult because polyvinyl carbazol is radicallypolymerized.

In other embodiments of the invention, one can introduce polymers oroligomers (so-called telecheles) which carry suitable reactive groups attheir ends. Since PPS is manufactured in very low molecular weightsduring initial manufacturing steps and is only processed into a highmolecular weight product during a second "roasting process" at about150° to 200° C., one can introduce a select oligomeric or low-molecularweight component with the aforementioned groups after the firstmaufacturing step (if need be, given a renewed addition of Na₂ S) forexample, in accordance with the following schematic equation: ##STR6##The co-condensed components would have to be added in the same amountrange as the stabilizer polymers (i.e. 0.1% up to approximately 5% masscomponent) so as not to alter the mechanical properties of PPS or othersulfur-containing resin.

The functional stabilizer groups selected for the co-condensationreactions are also present in low-molecular weight substances. However,problems occur with low-molecular weight additives when their boilingpoint is too low because they can then evaporate out of the reaction ordeposit on the surface of the parts as coatings. Further, suchlow-molecular weight substances cause problems when the migration rateis high (a danger of efflorescence is present with low-molecular weightsubstances); or when such substances can be washed out with water (whichis the case with humid storage conditions).

Suitable low-molecular weight substances which, however, must exhibitrelatively high mol masses are set forth below as representatives ofcorresponding material classes:

Carbazols, boiling point 354° . . . 355° C., corresponding to polyvinylcarbazol (Luvican), water insoluble.

Napthalic acid amides, melting point 307° . . . 308° C., correspondingto polyimide (Torlon) ##STR7##

Methoxy benzophenones, boiling point 354° . . . 355° C., correspondingto polyether ether ketone (PEEK) ##STR8## or, substituted diphenyl etherkyaphenine (triazine derivative) ##STR9## boiling point 350° C.; meltingpoint 231° C.

The foregoing highly conjugated substances are to be understood as beingrepresentatives of highly conjugated amines (carbazol), ketones(methoxybenzophenone), amides (naphthalic acid imide) and triazinederivatives (kyaphenine). As a result of their analogous structure tothe additive polymers, an effect corresponding to that shown by theseadditive polymers is attainable. However, a reduction of effect canoccur as a result of oxidation, for example, with carbazol andnaphthalic acid imides, over the NH group during processing. To thisdegree, representatives of this group of substances, which are treblysubstituted at their respective nitrogen atoms, are preferred to theN--H-compounds. The ketones and triazine derivatives do not exhibitthese disadvantages. In the case of triazine derivatives, nocorresponding technically usable polymer is presently known.

The greater mobility of the low-molecular weight substances favors themat low use temperatures, for example, at temperatures below 200° C. Thehigher migration capability (efflorescence) and possible evaporation inthe high processing temperature range, for example, at 370° C., makesthese kinds of material inferior to the polymer additives under certainconditions.

Substituted (sterically impeded) phenols, for example, phenolic resins,also appear to be fundamentally suited as stabilizers, however, theirthermal stability is not sufficient. The same also applies to otherinhibitors.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set forth and defined in thehereto-appended claims.

We claim as our invention:
 1. A method of reducing sulfur-containingexhaust gases from polyphenylene sulfide comprising:adding an effectiveamount of an additive material selected from the group consisting ofcondensable polymerizable aromatic ketones, condensable polymerizablearomatic amines, condensable polymerizable aromatic amides, andcondensable polymerizable aromatic imides in the form of reactivemonomers to base materials forming polyphenylene sulfide during themanufacturing process of polyphenylene sulfide, said effective amountbeing in the range of about 0.1% to about 5% by weight, based on theweight of said polyphenylene sulfide; and subsequently incorporatingsaid additive material into the polymer chain of polyphenylene sulfideas a copolymer, whereby at least some sulfur-containing exhaust gasesgiven off from said polyphenylene sulfide are absorbed by said additivematerial.
 2. A method as defined in claim 1 wherein said condensablepolymerizable aromatic ketones, amines, amides and imides are in theform of reactive oligomers.
 3. A method as defined in claim 2 whereinsaid reactive oligomers are added during a roasting process in themanufacture of polyphenylene sulfide and are subsequently incorporatedinto the polymer chain of polyphenylene sulfide as copolymers.
 4. Amethod of reducing sulfur-containing exhaust gases from polyphenylenesulfide comprising:adding an effective amount in the range of about 0.1%to about 5% by weight, based on the weight of polyphenylene sulfide, ofa relatively low molecular weight additive material having a boilingpoint greater than 300° C. to polyphenylene sulfide, said additivematerial being selected from the group consisting of polymerizablearomatic ketones, polymerizable aromatic amines, polymerizable aromaticamides and polymerizable aromatic imides, whereby at least somesulfur-containing exhaust gases given off from said polyphenylenesulfide are absorbed by said additive material.
 5. A sulfur-stabilizedresin material comprised of a sulfur-containing polymer having aneffective amount of an additive material selected from the groupconsisting of condensable polymerizable aromatic ketones, condensablepolymerizable aromatic amines, condensable polymerizable aromaticamides, and condensable polymerizable aromatic imides incorporated intothe polymer chain of said sulfur-containing polymer, said effectiveamount being in the range of about 0.1% to about 5% by weight, based onthe weight of said sulfur-containing polymer, whereby at least somesulfur-containing exhaust gases given off from said sulfur-containingpolymer are absorbed by said additive material.